Process for producing a solid lubricant self-supplying-type co-deposited metal film

ABSTRACT

A process for producing a solid lubricant self-supplying-type co-deposited metal film in which fine powder of inorganic polymer of graphite fluoride is dispersed in a metal plating bath in the presence of a co-deposition assisting surfactant having C - F bond in molecules selected from the group comprising cationic surfactants, nonionic surfactants and amphoteric surfactants which exhibit cationic characteristic at the pH value of a particular plating bath employed with or without levelling and brilliance imparting agents and a metal coating or film is deposited on a substrate so as to co-deposit graphite fluoride in the metal coating. A mechanical part having a graphite fluoride co-deposited metal coating thereon produced by the process. A metal plating bath employed in the process.

urosalti et a1.

[ PROCESS FOR PRODUCING A SOLID LUBRICANT SELF-SUPPLYING-TYPECO-DEPOSITED METAL FILM [22] Filed: Dec. 7, 1971 [21] Appl. No.: 205,726

52 us. Cl. 204/16, 204/181 [51] llnt. Cl... C23b 7/00, BOlk 5/00 [58]Field of Search... 204/16, 181; 252/9, 12, 12.2, 252/18 [56] ReferencesCited UNITED STATES PATENTS 1,702,927 2/1929 Bezzenberger 204/181 [1113,787,294 Jan. 22,, 1974 2,750,334 6/1956 Brown 204/51 PrimaryExaminer-T. Tufariello Attorney, Agent, or Firm-Nelson Littell et al.

57 ABSTRACT A process for producing a solid lubricant selfsupplying-typeco-deposited metal filin in which fine powder of inorganic polymer ofgraphite fluoride is dispersed in a metal plating bath in the presenceof a co-deposition assisting surfactant having C F bond in moleculesselected from the group comprising cationic surfactants, nonionicsurfactants and amphoteric surfactants which exhibit cationiccharacteristic at the pH value of a particular plating bath employedwith or without levelling and brilliance imparting agents and a metalcoating or film is deposited on asubstrate so as to co-deposit graphitefluoride in the metal coating. A mechanical part having a graphitefluoride codeposited metal coating thereon produced by the process. Ametal plating bath employed in the process.

4 Claims, No Drawings PROCESS FOR PRODUCING A SOLID LUBRICANT SELF-sUlPPLYllNG-TYPE CO-DEPOSITED METAL BACKGROUND OF THE INVENTION Thisinvention relates to novel and improved metal plated products havingthereon inorganic polymercodeposited coatings or films of solidlubricant selfsupplying-type and processes producing the same.

There have been proposed a number of processes for producing platedproducts having thereon inorganic polymer-co-deposited coatings or filmsof solid lubricant self-supplying-type. For example, there are disclosedin Japanese Patents Nos. 419,801 and 521,020 processes for producingsuch plated products wherein a metal substrate is deposited in a metalplating bath with the addition of an insoluble inorganic salt in a finepowder form in plating bath so as to have the deposited metal coating orfilm uniformly incorporate the fine particle inorganic salt therein.

However, either of the processes of these Japanese patents referred toabove is performed by the addition of fine powder of salt of aluminum,magnesium or strontium or an oxide of any of the materials to an acidicnickel plating bath. Although there is described in either of theJapanese patents that by the addition of such salts or oxides, nickelcoatings or films can be formed on the substrate surfaces having finepowdery material uniformly dispersed therein, the prior arts disclosedin these Japanese patents exclusively direct to decorative satin-likecoatings or films or undercoats for corrosion resistance chromiumplatings, but do not direct to co-deposited metal coatings of films ofsolid lubricant self-supplying-type to which .the present inventionpertains. Of late, the technology for codepositing fine powder ofmolybdenum disulfide on the metal-deposited substrate surfaces toprovide lubricative plated products has been proposed (for example, seethe Co-Deposited Nickel Molybdenum Disulfide Metal Finishing by GE. Vest& 11F. Baggarre, November 1967 and more particularly, pages 52-58thereof). Molybdenum disulfide has been employed as a solid lubricantbecause molybdenum disulfide has the layer structure in which each ofmolybdenum atoms is sandwiched between sulfuratoms, each molybdenum atomslides between the surfaces of the sulfur atoms and the molybdenum hasalow shearing strength. However, it has been known that molybdenumdisulfide is a hydrophilic compound and has disadvantages with respectto chemical-resistant properties and lubricating characteristics atelevated temperature and therefore, molybdenum disulfide is not asatisfactory codeposition material.

SUMMARY OF THE INVENTION We have found that although graphite fluorideis quite hard to be dispersed in both water and oil, the compound hasexcellent properties as a solid lubricant. And on the basis of thediscovery, we have exerted our efforts toward the utilization of theproperties of the compound as a solid lubricant in the field ofcodeposition plating and have reached the present invention whichpertains to the production of plated products having co-depositedcoatings of films of solid lubricant self-supplying-type. i

It has been found that when fine powder of an inorganic polymer ofgraphite fluoride (the material will be referred to simply as graphitefluoride" herein below) is dispersed into a conventional plating bath(the bath will be referred to as fundamental plating bath or compositionherein below) together with a surface active agent or surfactantselected having fluorine-carbon bond in their molecules (F-C bond)selected from the group comprising water soluble cationic surfactants,nonionic surfactants and amphoteric surfactants which exhibit cationiccharacteristics at the pH value of a particular plating bath employed,these surfactants perfectly wet' graphite fluoride of high waterrepellent property, disperse the graphite fluoride in the plating bathwith'stabilization and cause the fine particles of the graphite fluorideto become positively charged.

It has been experimentally determined that when a .metal platingoperation is conducted with the thus prepared plating bath, thepositively charged fine particles of graphite fluoride exhibit anelectrophoresis phenomenon subject to the force from the electric fielddeveloped between electrodes and move toward and onto the cathodeorworkpiece whereby the graphite fluoride particles are uniformlyco-deposited in the deposited metal coating or film on the workpiece.

It has been also determined that when a metal plating is conducted usingthe plating bath in which fine powder of graphite fluoride is uniformlydispersed in the presence of such a co-deposition agent having C-F bondin their molecules selected from the group comprising cationicsurfactants, nonionic surfactants and amphoteric surfactants whichexhibit cationic characteristics at the pH value of a particular platingbath employed under mechanical agitation such as screw-, liquidrecyclingor air agitation, the graphite fluoride is not only perfectlywetted, but the dispersion state of the graphite fluoride is quitestabilized. Furthermore,

since the thus obtained co-deposited coating or film is free ofbrittleness and has-an excellent electrification property and even ifthe plating bath contains graphite fluoride'in a low concentration, theco-deposited coating may contain a great mount of graphite fluoride asmuch as possible therein. Since solid lubricant self-supplying metalcoated products of the presentinvention have a high sliding propertywith less friction, they can find their application in inner walls ofcylinders, inner walls of engines, piston rings, piston rods, bearingsand slidable parts of other machines and are reliable in their functionsthroughout the service life. Thus, the present invention provide usefulmechanical parts or'members.

According to one aspect of the present invention, there is provided aprocess for producing a metal plated product having thereon aco-deposited coating or film of solid lubricant self-supplyin'g-typewhich comprises the steps of dispersing fine powder of inorganic polymerof graphite fluoride into a metal plating bath in the presence of afluorocarbon surfactant having fluorine carbon bond (F-C bond) in theirmolecules selected from the group comprising water soluble cationicsurfactants, nonionic surfactants and amphoteric surfactants whichexhibit cationic characteristics at the pH value of a particular platingbath employed, and depositing a metal coating or film on a substrate soas to codeposite graphite fluoride in the metal coating.

According to another aspect of the present invention, there is provideda plated product having a co deposited metal coating or film of solidlubricant selfsupplying-type produced by the process referred to above.

According to a still further aspect of the present invention, there isprovided a metal plating bath which comprises a conventional fundamentalmetal plating bath composition, fine powder of inorganic polymer ofgraphite fluoride and a fluorocarbon surfactant having fluorine carbonbond in their molecules (F-C bond) selected from the group comprisingwater soluble cationic surfactants, nonionic surfactants and amphotericsurfactants which exhibit cationic characteristics at the pH value of aparticular metal plating bath composition employed.

The graphite fluoride of the present invention can be prepared bycausing carbon or graphite to react with fluorine or a fluorine compoundat a temperature below 550C and is powder of an inorganic polymer of afluoride having the structure in which fluorine is introduced betweencarbon layers or layers constituting a lattice structure and the layershaving the fluorine therebetween are bonded together by covalent bondwith the valence electron of one free extra atom of the carbon atomswhich can be represented by the molecular formula (CF),.. Therefore, inthe graphite fluoride referred to above, the molar ratio of fluorine tocarbon is I11 and is a solid usually having a white or gray crystalstructure and a specific gravity of 2.45.

In addition, the graphite fluoride is characterized by that the compoundexhibits a high electric insulation, is almost free from attack fromchemicals, is not wetted with water and oil (contact angle of 145C) andwater and oil repellence and lubricity at elevated temperature.Furthermore, the graphite fluoride is stable in both acidic and basicmetal plating baths without sacrificing its characteristics as a solidlubricant. The graphite fluoride is further characterized by that thecompound can maintain its lubricity at elevated temperatures on theorder of 500C at which other solid lubricants would lose their lubricityand is stable against friction heat and environmental conditions presentin boundary lubrication. However, it has been known that when suchgraphite fluoride is dispersed and codeposited in deposited metal filmor coating, the greater the volume percentage of the compound is, thelower the adhesion of the compound to the deposited metal film is. Thus,it is preferably to limit the amount of graphite fluoride to beco-deposited in the solid lubricant self-supplying type deposited metalcoating or film of the present invention to the volume fraction up to 80percent at the most.

When the deposited metal coating or film is required to have a highmechanical strength or a metal deposited product having such a coatingis employed as a friction member or part such as a piston ring orbearing, codeposition of graphite fluoride in a substantial amount isobjectionable and it is preferably to limit the codeposition amount ofsuch a compound to a value up to 10 percent at the most.

And particles of graphite fluoride to be added to a metal plating bathcomposition are preferably in a finely divided powder so that theparticles may have good adhesion to the deposited metal coating. Thediameter of such particles is usually smaller than 10p. and it ispreferable that such particles contain about 80 percent of fineparticles having diameters smaller than 0.5 1 The amount of graphitefluoride to be added to the fundamental metal bath composition isusually less than 50 g/l with preference concentration within the rangeof 0.1-10 g/l.

As to fluorocarbon surfactants to be suitably employed as assistants inthe present invention, any member having fluorine carbon bond (C-F bond)in their molecules selected from the group comprising cationicsurfactants, nonionic surfactants and amphoteric surfactants whichexihibit cationic characteristics at the pH value of a particularelectroplating bath composition employed and for example, cationicsurfactants sold under the trade name FC-134 (a perfluorinatedquaternary ammonium compound) by Minesota Minning & ManufacturingCompany in the United States of America are preferably employed.However, when nonionic surfactants having C-F bond-are employed asassistants, graphite fluoride particles are positively electrified onlywhen the metal plating bath employed is of an acidic one.

On the other hand, when anionic surfactants having C-F bond in theirmolecules or amphoteric surfactants 1 which exhibit anioniccharacteristics at the pH value of a particular electroplating bathcomposition are employed as assistants, graphite fluoride particles arenegatively charged and these assistants obstruct codeposition of thegraphite fluoride particles to the deposited metal coating or film andtherefore, both of these types of surfactants cannot be suitableemployed in the present invention.

As to the amount of the fluorocarbon surfactant to'be added to thefundamental metal plating bath composition as an assistant forco-deposition, the amount of such a surfactant is preferably within therange of 5 mg/] to 5 g/l with respect to the bath composition with mostpreferable range of 10 mg/l to 500 mg/l. In carrying out the process ofthe invention, it has been found that the co-deposition operation isefficiently effected under mechanical agitation such as screw-, airorliquid recycling agitation. It has been also found that even when powderof graphite fluoride is dispersed in water in a different way fromco-deposition, the use of any one of the above-enumerated fluorocarbonsurfactants having the same chemical bond as that of graphite fluorideor the fluorine carbon bond (C-F) in its hydro phobic group is suitablyemployed as dispersion agent. Therefore, the present invention can bealso applicable to chemical platings in which particles of graphitefluoride are suspended in water or chemical plating baths by the use ofthe surfactants of the invention different from electroplatings.

As to metals in the coatings or films of which graphite fluoride can besuitably co-deposited according to the present invention, as appreciatedfrom the principle of the invention, all metals which can be depositedon cathodes or substrates by electroplating are useful. These metalsinclude copper, nickel, chromium, zinc, cadmium, tin, iron, lead, noblemetals and alloys thereof, for example. The pH of a particular platingbath employed is not related to whether the bath is acidic or alkaline.

PREFERRED EMBODIMENT OF THE INVENTION The present invention will be nowin detail described by way of specific example of the same, but itshould be understood that the invention is not limited to such films isincreased sufficientto enhance its wear resistance property.

EXAMPLE 1 1 An electroplating bath was prepared employing thefollowing'composition ingredientsz' Fine powder of graphite fluoride(average particle diameter of 02p.) 5 g/l Water soluble fluorocarboncationic surfactant FC134 (the trade name of a product sold by MinesotaMinning & Manufacturing Company in the United States of America) ppmNiSO -6H O 280 g/l NiCl -6H O 45 g/l H BO 40 g/l Asahilight SN1 (thetrade name of ,a commercially available brilliance imparting agent) 2000/1 Asahilight SN-2 (the trade name of a commercially availablebrilliance imparting agent) 2 cc/] The pH of the plating bath wasadjusted to 4.2 using sulfuric acid. A steel test piece mm in outerdiameter, 16 mm in inner diameter and 8 mm in thickness) for aNishihara-type wear-resistance testing machine was employed as thecathode and a nickel plating operation was performed under conditionssuch as bath temperature of 50C and current density of 5 A/dm for about50 minutes until the cathode was deposited thereon a graphitefluoride-codeposited coating up to the thickness of 50 1.1.. Forcomparison purpose, a control test piece of the same material waselectroplated using the same plating bath as that employed in the aboveplating operation except for the elimination of the graphite fluoridepowder and surfactant under the same plating conditions. Wear resistancetests were conducted on these plated test-pieces and the results of thetests are given hereinbelow.

Wearing procedure Rolling including 29.73 percent of sliding Load 30 kgRolling rate 613 r.p.m. Environment Dry wearing in the atmosphere Matingpiece Annealed carbon tool steel SK 5 TEST RESULTS required for wearingup to 50 mg From the above Table l,- it will be appreciated that thewear-resistance of the graphite fluoride-codeposited metal coating orfilm of the invention is substantially higher than that of the notco-deposited metal coating or film.

EXAMPLE 2 4 An electroplating bath was prepared employing the followingcomposition ingredients:

Fine powder of graphite fluoride (the average diameter of 0.2 p.) 5 g/lWater soluble fluorocarbon cationic surfactant FC-l34 20 ppm NiSO -6H O280 g/l NiCl -6H O 45 g/l H 40 g/l I Asahilight SN-l 20 cell AsahilightSN-2 2 cc/l The pH value of the plating bath was adjusted to 4.2 using H50 Eight SUJ-2 steel test pieces (in a doughnut forrn (40 mm in outerdiameter and 8 mm in thickness) for a roller-type friction testingmachine were employed as cathodes and a nickel plating operation wasperformed under screw agitation using plating conditions such as bathtemperature of 50C and current density of 5 A/dm for about 50 minutesuntil the cathodes were deposited thereon graphite fluoride-codepositednickel coatings or films of 5011.. For comparison purpose, thecorresponding number of control test pieces identical with thoseemployed in the codeposition plating operation mentioned just aboveusing the same nickel plating bath except for the elimination of theabove-mentioned graphite fluoride and fluorocarbon surfactant. All thethus treated test pieces were subjected to comparison tests for theircoefficients of friction in No. 1 additive turbin oil (JIS K 2213)friction From the above Table 2, it will be understood that the averagecoefficient of the graphite fluoride-codeposited nickel coatings of theinvention is smaller than that of the control nickel coatings having nographite fluoride co-deposited therein.

EXAMPLE 3 A plating bath was prepared employing the followingcomposition ingredients:

Fine powder of graphite fluoride (average particle diameter of 0.2 J.)10 g/l Water soluble fluorocarbon cationic surfactant FC-l34 20 ppm ISodium cyanate 147 g/l Copper cyanate 150 g/l Sodium hydroxide 40 g/lPotassium soda tartrate 211 g/l Lead acetate 75 g/] A brass bearingmaterial was employed as the cathode and a pure copper piece wasemployed as the an-- ode. The cathode was deposited thereon a copperlead alloy coating or film in which graphite fluoride was depositedunder screw agitation thickness using plating conditions such asbathtemperature of 60C and current density of 5 A/dm for about 50 minutes upto 50p..

The thus treated bearing material was found suitable as a bearing. Thetorque of the thus treated bearing material was found 32 percent lessthan that of the control which was treated in the same plating bathexcept for the elimination of the above-mentioned graphite fluoride andfluorocarbon surfactant and accordingly, the copper-lead alloy coatingon the control had no graphite fluoride co-deposited therein.

EXAMPLE 4 An electro-plating bath was prepared employing the followingcomposition ingredients:

Fine powder of graphite fluoride (average particle diameter of 0.2 .1.)10 g/l Water soluble fluorocarbon cationic surfactant -FC-l34 20 ppmLead borofluoride 243 g/l Fluoboric acid 23.3 g/l Boric acid 23.3 g/lGelatine 0.2 g/l The pH value of the plating bath was adjusted to 1.5using fluoboric acid. A brass bearing material was employed as thecathode a lead piece was employed as the anode and the cathode wasdeposited thereon a lead coating or film in which graphite fluroride wascodeposited under air agitation using plating conditions such as bathtemperature of 30C and current density of A/dm for about 20 minutes upto the coating thickness of 50a. The thus treated brass bearing materialwas found suitable as a bearing. A control bearing material formed ofthe same material was treated in the same plating bath except for theelimination of the above-mentioned graphite fluoride and fluorocarbonsurfactant therefrom. The two bearing materials were subjected toabrasion test in which the time required to wear the material to apredetermined amount was determined and it was found that the timerequired to wear the inventive material having the graphite fluorideco-deposited coating was about 4.5 times long as that for the control.This means that a machine or apparatus having the bearing with the leadcoating in which graphite fluoride is co-deposited has a service life atleast 4 times as long as the corresponding machine or apparatus havingthe control bearing.

EXAMPLE 5 An electroplating bath was prepared using the followingcomposition ingredients:

Fine powder of graphite fluoride (average particle diameter of 0.2a) g/lWater soluble fluorocarbon cationic surfactant FC-l34 20 ppm Silvercyanate 38 g/l Potassium cyanate 50 g/l Potassium hydroxide 125 g/lPotassium carbonate 44 g/l A pure silver piece was employed as the anodeand a brass bearing material was employed as the cathode. A silverplating operation was performed under screw agitation using platingconditions such as bath temperature of 35C and current density of 5 A/dmfor about 16 minutes to deposit a silver coating on the cathode in whichgraphite fluoride was co-deposited upto the thickness of 50p. The thustreated bearing material was found suitable for a bearing as in the caseof the products in Examples 3 and 4. When employed under light loadconditions, the wear of the graphite-co-deposited silver coating was onefifth as less as that of the control which had been treated in the sameplating bath except for the elimination of the above-mentioned graphitefluoride and fluorocarbon surfactant therefrom.

EXAMPLE 6 An electroplating bath was prepared using the followingcomposition ingredients:

Fine powder of graphite fluoride (average particle diameter of 2 p.) 5g/l Water soluble fluorocarbon non-ionic surfactant FC-170 (the tradename of a product sold by Minesota Minning & Manufacturing Company inthe United States of America) 30 ppm NiSO -6H O 280 g/l NiCl -6l-l O 45g/l H 40 g/l Asahilight SN-l 2O cc/l Asahilight SN-2 2 cc/l The pH valueof the plating bath was adjusted to 4.2 using H 80 The test pieceemployed in this example was a steel piece identical with that employedin Example l and a nickel plating operation was conducted under liquidrecycling agitation using plating conditions such as bath temperature of50C and current density of 5 A/dm about for 50 minutes to deposit anickel coating or film up to 50p thickness on the cathode havinggraphite fluoride co-deposited therein. A control formed of the sametype material was treated in the same plating bath except for theelimination of the above-mentioned graphite and fluorocarbon surfactantand accordingly, the resultant control had thereon a nickel coating inwhich no graphite fluoride co-deposited. The two types of test pieceswere subjected to wear resistance test to find that the inventive testpiece had a wear resistance 3 times as high as that of the control.

EXAMPLE 7 An electroplating bath was prepared using the followingcomposition ingredients:

Fine powder of graphite fluoride (average particle diameter of 0.5 p.)10 g/l Water soluble fluorocarbon amphoteric surfactant FC-l72 (thetrade name of a product sold by Minesota Minning & Manufacturing Companyin the United States of America) 0.1 g/l NiSO '6H O 280 g/l NiCl '6l-l O45 g/l H 80 40 g/l Asahilight SN-l 20 cc/l Asahilight SN-2 2 cell The pHvalue of the plating bath was adjusted to 4.2 using H 80 and the testpiece employed as the cathode in this example was a steel pieceidentical with that employed in Example 1. A nickel plating operationwas performed on the cathode under liquid agitation using platingconditions such as bath temperature of 50C and current density of 5 A/dmfor about 50 minutes to deposit a nickel coating or film on the cathodeup to 50 p. thickness having graphite fluoride co-deposited therein. Acontrol test piece formed of the same type of material as that employedin this example was treated in the same plating bath as that employed inExample 7 except for the elimination of the graphite fluoride andfluorocarbon surfactant to deposit a nickel coating thereon which had nographite fluoride codeposited therein. The two types of test pieces weresubjected to wear resistance test using the same procedure andconditions as mentioned in connection with Example 1. The result of thetest are given in Table 3 hereinbelow.

TABLE 3 Test piece Inventive Control test piece test piece Item formeasurement Number of rolling 17,500 3,000

required for wearing up to 50 mg As clear from the above Table 3, thegraphite-codeposited nickel coating exhibits a higher wear resistancethan the control in which no graphite fluoride.

l0 supplying-type co-deposited metal coating or film comprising thesteps of dispersing fine powder of inorganic polymer of graphitefluoride having an average particle diameter less than 10 ,u. in a metalplating bath in the presence of a cationic surfactant having fluorinecarbon bond in the molecule, said surfactant being water soluble, saidsurfactants perfectly wetting said graphite fluoride which has a highwater repellent property and dispersing said graphite fluoride in theplating bath with stabilization thereof and causing the fine powder ofsaid graphite fluoride to become positively charged, and electricallydepositing a metal coating or film on an electrically conductivesubstrate so as to co-deposit less than percent byvolume of graphitefluoride in said metal coating.

2. The process for producing a solid lubricant selfsupplying-typeco-deposited metal film as set forth in claim 1, in which the amount ofsaid surfactant is less than 5 g/l and in which the amount of saidgraphite fluoride is less than 50 g/l.

3. The process for producing a solid lubricant selfsupplying-type metalfilm as set forth in claim 1, in which said surfactant is aperfluorinated quaternary ammonium compound.

4. The process for producing a solid lubricant selfsupplying-type metalfilm as set forth in claim l, in which said metal plating bath furthercontains additive agents such as levelling and brilliance impartingagents.

2. The process for producing a solid lubricant self-supplying-typeco-deposited metal film as set forth in claim 1, in which the amount ofsaid surfactant is less than 5 g/l and in which the amount of saidgraphite fluoride is less than 50 g/l.
 3. The process for producing asolid lubricant self-supplying-type metal film as set forth in claim 1,in which said surfactant is a perfluorinated quaternary ammoniumcompound.
 4. The process for producing a solid lubricantself-supplying-type metal film as set forth in claim 1, in which saidmetal plating bath further contains additive agents such as levellingand brilliance imparting agents.